Selective Hydrogenation of Phenol to Cyclohexanone over a Highly Stable Core-Shell Catalyst with Pd-Lewis Acid Sites

Cyclohexanone is widely used in coatings, pesticides, dyes, lubricants, and other industries due to its high solubility and low volatility, but designing highly active and stable heterogeneous catalysts for selective hydrogenation of phenol to cyclohexanone is a still challenge. In this paper, core-shell structure Pd@Al-mSiO₂ catalysts containing a Pd metal core and an Al-modified mesoporous silica shell were design for hydrogenation of phenol to cyclohexanone. At 1 MPa, 1 h, and 100 °C, cyclohexanone with 98.5% of selectivity and 100% of phenol conversion was achieved over Pd@Al-mSiO₂ catalysts with trace aluminum modification. Pd cubes with (100) facets, as the hydrogenation active core, had higher cyclohexanone selectivity than nanoparticles with (111) facets, while mesoporous shells with abundant Lewis acid sites played an important role in activating aromatic rings and inhibiting carbonyl hydrogenation, and close metal–acid interfaces further enhance the synergy between multiple active sites. Moreover, owing to the protection of the shell, the catalyst could be repetitively used 5 times without any loss of catalytic activity.